1. Field of the Invention
The present invention pertains to an apparatus for applying coatings of particulate material to a workpiece by intermittent injection of discrete quantities of material into a combustion chamber and propelling the material through a nozzle entrained with comustion gases for impacting the workpiece.
2. Background Art
In the art of applying coatings of particulate materials to workpieces, methods and apparatus have been developed whereby discrete quantities of material are intermittently injected into a combustion chamber containing a fuel-air mixture, which mixture is ignited to produce heating of the material and propulsion of the material through a nozzle to be impinged on the workpiece. Coatings of powdered tungsten carbide, for example, have been successfully applied to workpieces using an apparatus and method of the general type described in U.S. Pat. No. 3,801,346 to Rosser B. Melton, Jr. et al and U.S. Pat. Nos. 3,893,578; 3,967,761; 3,974,939 and 4,096,945 to Rosser B. Melton, Jr. and Elbert M. Hubbard. These patents pertain to a system wherein an elongated tape is formed to have a plurality of spaced apart discrete capsules, each containing a predetermined quantity of particulate material such as powdered metal alloy. The tape is fed to a stripping device wherein the capsules are clamped and perforated with a jet of high pressure gas to propel the material into a combustion chamber in timed relationship to the ignition of a fuel-air mixture which is also injected into the combustion chamber. The resultant combustion of the mixture heats the particles of material and propels them from the combustion chamber through a nozzle at high velocity for impacting a workpiece to thus form a coating on the workpiece.
As a result of the further developement of a system of the general type described in the aforementioned patents the need for certain improvements has been realized. One problem with the prior art apparatus pertains to the arrangement of the clamping mechanism and the so called inlet and outlet manifolds which clamp and seal the tape around the respectivee capsules so that a jet of high pressure gas may be injected to pierce the tape to inject the particulate material into the combustion chamber. The need to provide an adequate seal around the periphery of the capsule and the need for reliable high speed stripping of the tape resulted in the development of a superior indexing mechanism for positioning and clamping the discrete capsules for subsequent stripping and injection of the material contained therein.
Other desiderata resulting from the development of the general type of apparatus of the present invention include the need for ease of replacement of expendable parts such as the material injection nozzle and the components which clamp the tape during the capsule stripping operation.
The provision of improvements in the tape indexing and stripping mechanism has also resulted in the need for modifications in the timing of the events which result in the delivery of the particulate material to the combustion chamber and the implementation of the combustion process.
The need for improvements in particulate material coating apparatus of the general type described herein has resulted in the present invention which is summarized and described in detail hereinbelow.